Process for crimping a tow of vinyl alcohol polymer



May 2, 1967 P. J. ER A TAL 3 ,316,611

PROCESS FOR CRIMPING A TOW OF VINYL ALCOHOL POLYMER Filed Feb. 24, 1965 P/rreK/eaw f rmz.

Gerard 1 /22/12 2;

lnvenlors A tlorneys' United States Patent France, as- France, a corpo- This invention relates to a process for mechanically crimping a tow of continuous or discontinuous filaments of a vinyl alcohol polymer.

By vinyl alcohol polymer are meant vinyl polymers whose chain comprises at least 50% by number of units at least some of these units being acetalised.

The term degree of humidity or water content will be used to denote the quantity of water retained by the tow, either on moistening in a gaseous atmosphere or after immersion in water, this quantity being assessed as a percentage of the total mass of the moist tow. The term degree of sorption of water of the tow will be used to denote the quantity of water retained by 100 g. of the tow (reckoned as dry) after it has been brought to hydrometric equilibrium with a particular gaseous atmosphere. It is thus to be distinguished from the degree of swelling, which is the quantity of water retained by a tow after immersion in water followed by centrifuging, also reckoned on 100 g. of the dry tow.

It is known that the mechanical crimping of tows of synthetic filaments is advantageously effected after a thermal treatment, in the course of which the tow enters a bath of hot water or of another liquid containing hydroxyl groups, which is at a temperature of 50-150 C. Under these conditions, the tow has, on entering the crimping zone, a very high degree of humidity (up to 87.5%), due to the presence of swelling water and of capillary water.

Experience has shown that this type of treatment is not applicable to tows of filaments consisting of vinyl alcohol polymers, because they are damaged thereby.

It is an object of the present invention to provide a mechanical crimping process involving humidification of the tow at an elevated temperature which is useful with tows of vinyl alcohol polymer.

The process of the invention comprises humidifying a tow consisting of continuous or discontinuous filaments of a vinyl alcohol polymer with water vapour under conditions such that no liquid water comes into contact with the tow and that the tow coming from the humidifying treatment is at a temperature between 70 and 150 C. and has a degree of humidity at least 2% and at most equal to the degree of sorption, immediately thereafter mechanically crimping the tow in a compression chamber heated at a temperature such that the temperature of the tow in the chamber is between 80 an 150 C., and then cooling the tow while it is still in the compressed state.

The humidifying treatment must be carried out in an atmosphere comprising water vapour free from water droplets. It is advantageously carried out by passing the tow over the surface of a body, e.g. a layer of water heated for example by a heating jacket which completely surrounds the humidifying vessel; water is chosen in preference to other liquids for reasons of economy. Un- :ler these conditions, the water vapour humidifies the tow throughout. The temperature of the body of water must be above C. and it is advantageously between 80 and C., but temperatures above 100 C. might in some cases be applied by heating with pressurised steam in a zone which can be maintained under pressure. The humiditying treatment imparts to the tow a water content below or at most equal to its degree of sorption at the temperature and the relative humidity obtaining during the operation, and in any case well below that represented by the degree of swelling which results when the same tow is wetted in a bath in accordance with the prior art.

The humidifying operation may for example be carried out in a heated chamber containing a mixture of air and expanded steam, in appropriate, continuously adjusted proportions, taking the precautions necessary for avoiding contact of condensed water droplets with the tow.

The degree of humidity of the humidifying atmosphere may vary within wide limits in accordance with its temperature and the temperature and degree of humidity desired for the tow. Usually it is advantageously in the the neighborhood of 80%.

The duration of the time of contact of the tow with the humidifying atmosphere may vary within wide limits, for a given water content, but must generally be above 2.5 seconds. Generally speaking, the higher the temperature attained by the tow, the lower can its degree of humidity be.

The hot crimping operation can be carried out by the known method in a compression chamber, except that the rollers of the compression chamber are heated by any appropriate means, as by electric resistance heaters or by steam circulation, in order to produce a surface temperature of 80150 C.

Finally, the tow is cooled to a temperature below 50 C. in the compressed state; this may be done in a cooling zone which forms part of the compression chamber. The necessary cooling time may readily be determined in accordance with the operating conditions of the crimping device, including the temperature of the compression chamber, and also the state and properties of the tow (temperature, rate of travel, degree of sorption, count etc.).

A form of apparatus suitable for carrying out the process of the invention is illustrated diagrammatically in the accompanying drawing.

Referring now to the drawing, a tow 1 passes over a roller 2 and is then humidified in apparatus 3, which contains in its lower part a layer of hot water. The moist tow then passes over a roller 4, between rollers 5 of a compression chamber 6, and finally into a cooling zone '7. The crimped tow is collected in a receptacle 8.

The following examples illustrate the invention.

Example I A tow of 89,000 decitex (80,000 denier), 1.55 dtex/filament (1.4 denier per filament) enters and passes through the humidifier illustrated in the drawing under the following conditions:

It then enters a crimping apparatus of the compression chamber type at a speed of 26 in. per minute, the temperature of the heating rollers being C.

The tow then enters a zone formed by a prolongation of the compression chamber and cooled by circulation of a cold water. Its residence time in this zone is 45 seconds.

The tow obtained has the following characteristics:

Percent Initial crimp (F 20 Residual crimp after decrimping (F 10 F1/Fo:0.5 The degree of crimp were determined under the conditions indicated by BISFA (Bureau International de Standardisation des Fibres Artificielles et Synthetiques) in the pamphlet published by this body in 1956.

The formula applied is:

Degree of erimp= X 100 in which L =length of the crimped fibre (determined under. a tension equal to the weight of 5 m. of the fibre) L =length of the decrimped fibre (i.e. the length after application of a tension corresponding to the weight of 1000 m. of the fibre).

The formula is applied as such for the determination of F (initial crimp).

The residual crimp after decrimping (F is determined by replacing L in the above formula by L being the length to which the fibre returns when again subjected to a tension equal to the weight of 5 m. of the fibre after the measurement of L I Example II The same treatments as in Example I are applied to a tow of 352,000 dtex (320,000 denier), but under the following conditions:

Temperature of the Water C The tow obtained has the following characteristics:

Percent Initial crimp (F 12.4 Residual crimp after decrimping (F 8.1

We claim:

1. Process for the continuous production of crimped tows consisting of filaments of vinyl alcohol polymers, which comprises simultaneously humidifying the tow and raising its temperature to between 70 and 100 C. by contacting it with water vapour free from droplets of liquid water whereby the tow acquires a degree of humidity at least 2% and at most equal to the degree of sorption, immediately thereafter mechanically crimping the tow at a temperature of -150 C. in a heated compression chamber, and then cooling the tow while it is still in a compressed state.

2. Process according to claim 1, wherein a tow of continuous filaments is crimped.

3. Process according to claim 1, wherein a tow of discontinuous filaments is crimped.

4. Process according to claim 1, wherein the tow is humidified and heated by passing it through a space above the surface of a body of water which is at a temperature of 80100 C.

5. Process according to claim 1, wherein the tow is humidified and heated by passing it through a heated chamber containing a mixture of water vapour and air in predetermined proportions.

6. Process according to claim 5, wherein the heated chamber contains air of relatively humidity approximately 80% and at a temperature of approximately C.

7. Process according to claim 1, wherein the tow is subjected to the humidifying conditions for at least 2.5 seconds.

8. Process according to claim 4 wherein the tow is subjected to the humidifying conditions for at least 2.5 seconds.

9. Process according to claim 6, wherein the tow is subjected to the humidifying conditions for at least 2.5 seconds.

10. Process according to claim 1, wherein in the crimping operation the humidifier tow is forwarded by rollers heated to a temperature of 80-150 C.

11. Process according to claim 8, wherein in the crimping operation the humidified tow is forwarded by rollers heated to a temperature of 50-150 C.

12. Process according to claim 9, wherein in the crimping operation the humidified tow is forwarded by rollers heated to a temperature of 80 C.

13. Process according to claim 1, wherein the tow is cooled to below 50 C. while still in a compressed state.

References Cited by the Examiner UNITED STATES PATENTS 2,575,781 11/1951 Baraeh 19-66 2,575,839 11/1951 Rainard 19-66 3,041,705 7/1962 Sonnino 281 3,111,740 11/ 1963 Stanley 281 3,152,379 10/1964 Osban 281 3,174,208 3/ 1965 Eaito et al. 2872 MERVIN STEIN, Primary Examiner.

L. K. RIMRODT, Assistant Examiner. 

1. PROCESS FOR THE CONTINUOUS PRODUCTION OF CRIMPED TOWS CONSISTING OF FILAMENTS OF VINYL ALCOHOL POLYMERS, WHICH COMPRISES SIMULTANEOUSLY HUMIDIFYING THE TOW AND RAISING ITS TEMPERATURE TO BETWEEN 70* AND 100*C. BY CONTACTING IT WITH WATER VAPOUR FREE FROM DROPLETS OF LIQUID WATER WHEREBY THE TOW ACQUIRES A DEGREE OF HUMIDITY AT LEAST 2% AND AT MOST EQUAL TO THE DEGREE OF SORPTION, IMMEDIATELY THEREAFTER MECHANICALLY CRIMPING THE TOW AT A TEMPERATURE OF 80*-150*C. IN A HEATED COMPRESSION CHAMBER, AND THEN COOLING THE TOW WHILE IT IS STILL IN A COMPRESSED STATE. 